“He may be a successful manager, but he must learn — even at his age — to become a good man manager. At the moment we have to say he’s not man managing that team.

“When you see people smiling, it’s amazing how much more they will do. There’s not enough players smiling in that Manchester United team – and there’s a little bit of a fear factor attached to mistakes now.

“All those players he’s got are not bad players and they’ve not played negative football all their lives. He’s being incredibly stubborn.”

Parker highlighted summer signings Anthony Martial and Memphis Depay as two players who are underperforming at Old Trafford.

United spent an initial £60million-plus on the duo but they have flickered only intermittently, and the former right-back believes that is the manager’s fault.

“I look at Martial and worry for him,” added Parker. “He looks like a boy who doesn’t smile any more. He doesn’t look like he’s enjoying himself.

“The form Memphis Depay is showing hasn’t just happened because he’s playing in the Premier League. That boy probably feels like a scapegoat. He’s in a country relatively close to where he’s from, but feeling a million miles away.”

Red flag: Paul Parker says Depay does not appear to be enjoying his football

United have been the Premier League’s biggest spenders in the last two summer transfer windows but Parker questions whether Van Gaal should be given vast money to spend next year.

He said: “Would you want Van Gaal to have another pot of gold in the summer? It doesn’t matter how good the players are if they’re not managed properly.

“At the moment there are a lot of very, very good players at Manchester Unitd — and the best isn’t being brought out of them.”